The French Interior Minister (Bernard Cazeneuve) called upon all French people to act as "patriotic citizens" to serve service in the security forces. It won't matter if you have military training or background, but it might be plus-up if you were a former soldier in the French army.
I looked it up....the operational reserve is made up of about 12,000 volunteers currently.....three-quarters of them are with the paramilitary police and the remainder in the regular police.
Currently, they have no right to a uniform, based on French law. There is an assigned rank system within the volunteer system. And they are eligible for various decorations.
My humble guess is that there will be some movement on expanding the definition of operational reserve....allowing gun licenses to occur through some simplified rules, and that a form of open-carry (common in the US) might emerge out of this if you were a patriotic citizen in the reserve force. Instead of roughly 1.2 million soldiers and regular police.....imagine another five million French reservists with weapons on the streets.
Limits to enter such a force? If you have a criminal record or behavior issues.....you'd probably be denied entry into the reserve force. I would imagine at least 10-percent of French society won't pass the entry point because of some crime issues in their past, or lack of emotional control.
The EU might be disturbed by this enlargement of the reserve force but it's about the only method left that would give the public some confidence that they were fixing the problem.